drm/etnaviv: make clock handling symetric between runtime resume and suspend

Currently the clock is enabled in the runtime resume function, but are
disabled a level further down in the callstack in the suspend function.
Move the clock disable into the suspend function to make handling
symmetrical between resume and suspend.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>